Signals have been traditionally processed in the electrical domain. However, conversion of optical signals to electrical signals is non-trivial at high modulation frequencies. Optical processing of optical signals provides an efficient and cost-effective approach at high modulation frequencies, e.g. when the modulation frequency is in the order of 40 GHz or higher.
Optical signal processing may be used e.g. for the recovery of clock frequency from an optical data signal.
The article “Optical Tank Circuits Used for All-Optical Timing Recovery”, by M. Jinno and T. Matsumoto, IEEE Journal of Quantum Electronics Vol. 28, No. 4 April 1992, pp. 895-900, discloses a method for optical clock recovery. An optical clock signal synchronized to an incoming data stream is generated by extracting line spectral components in the incoming data stream using an optical resonator whose free spectral range is equal to the incoming data bit rate.